GB2144143A

GB2144143A - Refining of palm oils

Info

Publication number: GB2144143A
Application number: GB08416478A
Authority: GB
Inventors: Peter Armin Thomas Swoboda
Original assignee: INSTITIUT PENYELIDIKAN MINYAK
Current assignee: INSTITIUT PENYELIDIKAN MINYAK
Priority date: 1983-06-28
Filing date: 1984-06-28
Publication date: 1985-02-27
Also published as: GB8416478D0; GB2144143B

Abstract

A palm oil or palm oil fraction is purified by a process involving the solvent extraction of the oil with an alcohol, optionally in admixture with up to 25% water, and a subsequent alkali wash and/or bleaching of the raffinate or an oil derived therefrom. The preferred solvents are azeotropic mixtures of ethanol or isopropanol with water. The refining of difficultly refinable fractions, such as palm oil stearins, is significantly facilitated by the alkali wash of the raffinate.

Description

SPECIFICATION Refining of palm oils The present invention relates to a process for the refining of palm oil and palm oil fractions.

Palm oil needs to be subjected to a process of refining after it has been extracted from the oil bearing fruit. As first extracted, the crude palm oil has a deep red colour and a characteristic odour. Conventionally, steps are taken during refining to remove the odour and, generally, also to remove the colour.

The refining process can be chemical or physical. Chemical refining, in which free fatty acids are removed by neutralisation, has been superceded in the palm oil industry at least in Malaysia by physical refining. In physical refining as practised at present, the palm oil is first gum conditioned by treatment with phosphoric acid, then contacted with activated bleaching earth, and subsequently deodorised by vacuum high temperature steam stripping to distil out free fatty acid and simultaneously thermally bleach the oil. The resultant product is known as RBD (i.e.

refined, bleached and deodorised) palm oil.

It has been known since before 1921 (seen U.S. Patent No. 1371342) that free fatty acids can be removed from fats and oils such as rape oil or cocoanut oil by solvent extraction with aqueous alcohol. In 1946 (see U.S. Patent No. 578751), it was proposed to extract with alcohol or aqueous alcohol free fatty acids from fats and fatty oils, including inter alia palm oil, for the preparation of alkyl esters and to facilitate alcoholysis of the residual fat or fatty oil.

However, to the best of our knowledge, such solvent extraction of free fatty acids has not been employed in the refining of crude palm oil or palm oil fractions.

It has now been found that, surprisingly, solvent extraction of palm oil or palm oil fractions with alcohol or aqueous alcohol is of particular use in the physical refining of said oil or fractions. Such extraction not only reduces the energy requirements of free fatty acid removal but also provides a raffinate having unexpected properties. In particular, the raffinate is more readily bleachable than could have been predicted. It also is of significantly reduced odour and flavour but retains a relatively high carotenoid content. Further, when the raffinate is subjected to an alkali wash, the refining of difficulty refinable fractions such as certain palm oil stearins is significantly facilitated.

According to the present invention, there is provided a process for the refining of a palm oil or palm oil fraction which process comprises the steps of (a) subjecting the oil to solvent extraction with an alcohol, optionally in admixture with up to 25% by weight of water, and (b) bleaching the raffinate of said solvent extraction or an oil derived therefrom.

The residual solvent can be removed from the raffinate by, for example, distillation and subsequent vacuum stripping which may be assisted by prior water washing. However, the removal of the residual solvent usually will be carried out during or after bleaching or other subsequent treatment steps.

The process of the invention has particular, but not exclusive, application, to crude palm oil.

However, the process can be applied to other grades of palm oil and palm oil fractions, for example palm olein, palm stearin or POMF (i.e. palm oil mid fraction). In particular, it is of use with difficulty refinable fractions such as certain palm stearins.

Preferably, the extracting solvent is a mixture of ethanol and water, or a mixture of isopropanol and water. Such mixtures of these alcohols and water are preferably of an azeotropic composition. The azeotrope of water and ethanol contains approximately 4.5% of water and has a boiling point of 78"C. The azeotrope of isopropanol and water has a water content of about 12% and a boiling point of 80"C.

The presence of water in the solvent reduces the extent of solubility of the oil in the solvent and hence improves the selectivity of the solvent extraction. Accordingly, it is preferred that the extracting solvent contains water. Up to 25% water can be used but it is preferred that the water content should be less than 20%, especially between 3% and 15%. Azeotropic mixtures are preferred because of the advantages of such mixtures in the recycling of the solvent during the process.

In the solvent extraction step according to the invention, components making up approximately 5% to 30%, especially 15% to 25%, of the original weight of the oil are preferably extracted into the extracting solvent. In the case of crude palm oil, substantially the whole benefit to be obtained by solvent extraction can usually be obtained in extracting components making up about 20% of the weight of the oil into the solvent.

The process is preferably carried out at a temperature which is as low as possible having regard to the melting point of the oil in order to avoid unnecessary use of energy and in order to obtain a high selectivity in the extraction. However, the maximum temperature to be employed will generally be dictated by the boiling point of the solvent. Usually, the temperature used will be within 20"C, preferably 10"C, of the melting point of the oil/solvent mixture. Use of higher temperatures will tend to increase the speed of the extraction but will tend to reduce the selectivity of the extraction process.

In the case of crude palm oil, it is preferred to carry out the process at a temperature of from 50 to 60"C.

The extraction is preferably carried out continuously. Suitably on a small scale, the extracting solvent is introduced into the bottom of a vessel containing the oil to be treated and rises as finely dispersed droplets therethrough to an overflow from the vessel from which the solvent containing extracted components of the oil is taken to a still from which the solvent is recovered and from which the extracted components may periodically be removed. However, on a commercial scale, it is preferred to employ countercurrent flows of the oil and solvent. For instance, purified oil, or raffinate, may be extracted from the base of the vessel whilst fresh oil to be treated is introduced at the top of the vessel so that there is a countercurrent extraction in progress continuously.

We have found that crude palm oil subjected to solvent extraction in this manner may produce a raffinate containing a concentration of carotenoids which is similar to, and may even be greater than, the concentration of carotenoids in the crude palm oil. The extraction may remove phospholipid and other polar gums. Some phosphorous compounds of a non-polar nature tend to remain in the refined oil but these are generally easy to remove during subsequent physical refining or by alkali washing.

The solvent extracted palm oil may be of considerable value without further substantial refining by virtue of its high carotenoid content, absence of odour and flavour, and low free fatty acid level. Since the oil at this stage generally has a pronounced red colour, it may be employed as a colouring material of natural origin. It may also be employed to provide a dietary source of vitamin A precursor.

The extract obtained from crude palm oil will generally contain substantial concentrations of free fatty acids and/or other compounds which are undesirable in the oil but which may be valuable in their own right. In particular, high free fatty acid oil can be used as, for example, animal feeds or feedstock for the oleochemical industry, especially in the catalytic conversion to esters useful as diesel fuel substitutes. Free fatty acids concentrates may be easily obtained from the extract by simple reduction of temperature.

Although crude palm oil is deeply coloured, it is, as has been said above, bleachable.

However, the bleachability of the oil is dependent upon its initial quality. The oil may be rendered difficult or impossible to bleach satisfactorily by auto-oxidation or because of impurities derived from the palm fruit during bad processing. We have found that crude palm oil treated by solvent extraction in accordance with the present invention has extremely good bleachability leading to a very light coloured fully refined product. In the case of poor quality crude palm oil, it may be necessary to subject the raffinate to alkali washing, for example, washing with aqueous sodium bicarbonate or, preferably, with aqueous sodium hydroxide, to remove the colour or colour precursors.

The bleachability of the raffinate or an oil obtained therefrom can be measured by the SCOPA (Seed Crushers and Oil Producer's Association) bleachability test. The test is as follows: 1. Heat 100 gm of the oil to be tested to 90"C with agitation under nitrogen blanket. Add 0.5 ml of 20% w/w of reagent grade citric acid in water and maintain at 90"C for 10 minutes 2. Add 2% of Tonsil Standard FF bleaching earth (2gm), raise temperature to 105"C and maintain under nitrogen blanket for 1 5 minutes.

3. Filter the hot oil earth mixture into a preheated 500 ml Buchner flask, through a Whatman No: 1 filter paper. Filter aid should not be necessary.

4. Transfer 90 + 1 gm of the filtrate to a 250 ml round bottomed flask, add a new antibumping granules, and draw a vacuum of 1-2 mm Hg. Heat mixture, without agitation, to 260"C + 1 C within 10 mins and maintain for 20 minutes.

5. Cool under vacuum as rapidly as is possible and safe to do.

6. When cooled to 60"C release the vacuum and measure the colour in a 1 3.4 cm (5i") Lovibond cell, using the BS 684/FOSFA method.

7. The test must be completed within 2+ hrs. of starting to degum.

In a modification of the above procedure, the treatment with bleaching earth is omitted to provide a "break" type bleachability test procedure.

Commercially, the bleaching step of the process of the invention usually will be carried out by the conventional bleaching process of treatment with bleaching earths and/or heat treatment such as steam distillation or vacuum steam stripping.

The palm oil can be subjected during refining to other conventional refining techniques such as gum conditioning, filtration, and polishing. Suitably, fractionation into olein and stearin fractions can take place after the solvent extraction step and optionally after the bleaching step.

The solvent extraction step of the present invention, by removing minor and trace constituents, may also greatly improve the efficiency of subsequent fractionation techniques in suitable cases.

The invention is illustrated by the following Examples.

Example I 200 g of crude palm oil were subjected to liquid/liquid extraction using an azeotropic mixture of ethanol and water in a batch process. The extracting solvent was introduced to the base of a container for the oil. The extracting solvent rose through the oil to an overflow from which it was conducted to a still where the azeotrope was recovered by distillation for recirculation to the container. The extraction was carried out with the oil at a treatment temperature of 55"C for a period of six hours. It was found that approximately 20% of the weight of the oil had been extracted at the end of the six hour treatment. Similar extractions were carried out for shorter and longer periods to extract lesser and greater percentages by weight of the starting oil. In each case, the raffinate was bleached by the SCOPA test procedure described previously.

The effect of the solvent extraction on the free fatty acid content (% FFA) of the oil and upon the bleachability of the oil, as measured as residual colour by the SCOPA bleachability test are shown in Table 1 below.

TABLE 1 Changes in raffinate content of FFA, and colour after the SCOPA bleachability test

% WEIGHT % FFA SCOPA 13.4 EXTRACTED (as palmitic) LOVIBOND cm RED YELLOW 0 (CPO) 2.83 13.6 0.65 20.5 0.20 36.6 0.09 CP0 = Crude Palm Oil The oil tested above was a commercial grade crude palm oil.

The oil after subjection to the solvent extraction described above to the extent of extracting 20% by weight of the oil was found to be essentially without the characteristic taste of crude palm oil. The purified product had a bland odour with no after taste. The extract in azeotropic alcohol however did exhibit the characteristic flavour of crude palm oil. Any residual alcohol in the purified oil was found to be removable by low temperature vacuum distillation assisted by water washing.

It was found that only about 15% by weight of the original carotene content of the oil had been extracted by the time that 20% of the weight of the oil had been extracted so that the residual carotene concentration of the refined oil was in fact increased.

The solvent extraction extracted the components giving rise to residual colour upon bleaching to a large extent. The presence of these compounds was demonstrable in the extract showing that they had been extracted rather than destroyed.

Example 2 The procedure of Example 1 was substantially repeated using (a) best quality crude palm oil, (b) normal quantity crude palm oil, (c) poor quality crude palm oil, and (d) poor quality crude palm stearin. However, in the case of samples (c) and (d) an alkali wash of the raffinate with 5N aqueous sodium hydroxide was effected before bleaching.The results are set forth in Table 2 below TABLE 2

SAMPLE DOBI % FFA SCOPA BLEACHED RED YELLOW (a) 3.4 1.5 0.8 10 raffinate of (a) - 0.06 0.4 10 (b) 3.2 3.8 1.7 17 raffinate of (b) - 0.22 0.6 7 (c) 1.4 6.2 11.1 70 raffinate of (c) - 0.23 6.2 63 alkali-washed raffinate of (c) - 0.05 3.5 35 (d) - 3.1 12.5 79 raffinate of (d) - 0.21 11.0 79 alkali-washed raffinate of (c) - 0.05 0.7 7 Example 3 The procedure of Example 1 was substantially repeated using a good quality crude palm oil and including an alkali wash of the raffinate with 5N aqueous sodium hydroxide. The results are set forth in Table 3 below: SAMPLE SCOPA BLEACHED RED YELLOW Crude Palm Oil 1.3 13 Raffinate 0.7 9 Alkali-washed raffinate 0.6 8 Example 4 The procedure of Example 1 was substantially repeated with the differences that (i) the treatment with bleaching earth was omitted: and (ii) samples of the raffinate were subjected to washing with water, citric acid, 1 N sodium bicarbonate, 1 N sodium carbonate, 5N sodium hydroxide or 0.3N sodium hydroxide. The results are set forth in Table 4 below: TABLE 4 SAMPLE "BREAK" TYPE BLEACHED RED YELLOW Crude Palm Oil 7.1 70 Raffinate 5.1 51 Water-washed raffinate 3.8 38 Citric acid washed-raffinate 4.2 42 Sodium bicarbonate-washed raffinate 3.3 33 Sodium carbonate-washed raffinate 2.2 22 Sodium hydroxide (5N) -wassed raffinate 1.6 16 Sodium hydrohide (0. 3N) -washed raffinate 1.8 18

Claims

1. A process for the refining of a palm oil or palm oil fraction, which process comprises the steps of (a) subjecting the oil to solvent extraction with an alcohol, optionally in admixture with up to 25% by weight of water, and (b) bleaching the raffinate of said extraction or an oil derived therefrom.

2. A process as claimed in Claim 1, wherein the raffinate or an oil derived therefrom is subjected to an alkali wash before bleaching.

3. A process as claimed in Claim 2, wherein the alkali wash is with aqueous sodium carbonate.

4. A process as claimed in Claim 2, wherein the alkali wash is with aqueous sodium hydroxide.

5. A process as claimed in any one of the preceding Claims, wherein the oil is crude palm oil.

6. A process as claimed in any one of Claims 1 to 4, wherein the oil is palm olein.

7. A process as claimed in any one of Claims 1 to 4, wherein the oil is palm stearin.

8. A process as claimed in any one of Claims 1 to 4, wherein the oil is palm oil mid fraction.

9. A process as claimed in any one of the preceding Claims, wherein the extracting solvent is a mixture of ethanol and water.

10. A process as claimed in any one of Claims 1 to 9, wherein the extracting solvent is a mixture of iso-propanol and water.

11. A process as claimed in Claim 9 or Claim 10, wherein the mixture is an azeotropic mixture.

1 2. A process as claimed in any one of Claims 1 to 10, wherein the water content of the extracting solvent is up to 20% by weight.

1 3. A process as claimed in Claim 1 2 wherein the water content is 3% to 15% by weight.

14. A process as claimed in any one of the preceding Claims, wherein there is extracted in Step (a) from 5 to 30% of the weight of the oil.

1 5. A process as claimed in Claim 14, wherein 1 5 to 25% by weight of the oil is extracted in Step (a).

16. A process as claimed in Claim 15, wherein about 20% of the weight of the oil is extracted in Step (a).

1 7. A process as claimed in any one of the preceding Claims, wherein Step (a) is carried out at a temperature within 20"C of the melting point of the oil/solvent mixture.

1 8. A process as claimed in Claim 17, wherein the oil is crude palm oil and Step (a) is carried out at a temperature of from 50 to 60"C.

1 9. A process as claimed in Claim 1, wherein the solvent extraction is substantially as hereinbefore described in Example 1.

20. A process as claimed in Claim 1, wherein the solvent extraction is substantially as hereinbefore described in Example 2.

21. A process as claimed in Claim 1, wherein the solvent extraction is substantially as hereinbefore described in Example 3.

22. A process as claimed in Claim 1, wherein the solvent extraction is substantially as hereinbefore described in Example 4.

23. A purified palm oil or palm oil fraction obtained by a process as claimed in any one of the preceding Claims.

24. A process for the refining of a palm oil or palm oil fraction, which process comprises the steps of (a) subjecting the oil to solvent extraction with an alcohol, optionally in admixture with up to 25% by weight of water, and (b) subjecting the raffinate or an oil derived therefrom to an alkali wash.

25. A process as claimed in Claim 24, wherein the alkali wash is with aqueous sodium carbonate.

26. A process as claimed in Claim 24, wherein the alkali wash is with aqueous sodium hydroxide.

27. A process as claimed in any one of Claims 24 to 26, wherein the oil is crude palm oil.

28. A process as claimed in any one of Claims 24 to 26, wherein the oil is palm olein.

29. A process as claimed in any one of Claims 24 to 26, wherein the oil is palm stearin.

30. A process as claimed in any one of Claims 24 to 26, wherein the oil is palm oil mid fraction.

31. A process as claimed in any one of Claims 24 to 30, wherein the extracting solvent is a mixture of ethanol and water.

32. A process as claimed in any one of Claims 24 to wherein the extracting solvent is a mixture of iso-propanol and water.

33. A process as claimed in Claim 31 or Claim 32, wherein the mixture is an azeotropic mixture.

34. A process as claimed in any one of Claims 24 to 32, wherein the water content of the extracting solvent is up to 20% by weight.

35. A process as claimed in Claim 34 wherein the water content is 3% to 15% by weight.

36. A process as claimed in any one of Claims 24 to 35, wherein there is extracted in Step (a) from 5 to 30% of the weight of the oil.

37. A process as claimed in Claim 36, wherein 1 5 to 25% by weight of the oil is extracted in Step (a).

38. A process as claimed in Claim 37, wherein about 20% of the weight of the oil is extracted in Step (a).

39. A process as claimed in any one of Claims 24 to 38, wherein Step (a) is carried out at a temperature within 20"C of the melting point of the oil/solvent mixture.

40. A process as claimed in Claim 39, wherein the oil is crude palm oil and Step (a) is carried out at a temperature of from 50 to 60"C.

41. A process as claimed in Claim 24, wherein the solvent extraction is substantially as hereinbefore described in Example 1.

42. A process as claimed in Claim 24, wherein the solvent extraction is substantially as hereinbefore described in Example 2.

43. A process as claimed in Claim 24, wherein the solvent extraction is substantially as hereinbefore described in Example 3.

44. A process as claimed in Claim 24, wherein the solvent extraction is substantially as hereinbefore described in Example 4.

45. An alkali-washed palm oil or palm oil fraction obtained by subjecting a palm oil or palm oil fraction to solvent extraction with an alcohol, optionally in admixture with up to 25% by weight of water, and subjecting the raffinate or an oil derived therefrom to an alkali wash.

46. An alkali-washed palm oil or palm oil fraction as claimed in Claim 45, wherein the solvent extraction and/or alkali wash is conducted in the manner specified in any one of Claims 25 to 44.